A common mode of interaction with printed images is to sort a large collection into sub-collections by placing them into piles. Many different sorts of categories can be used, for instance, separating piles by who is in them, by the day they were taken, by the location they were taken, by their predominant color, by the kind of object that features most prominently, or by any other appropriate scheme. A person might desire to organize digital images in the same way. This can be a daunting task for a digital photographer, as it is typical to have a very large number of images in a given collection and a limited size display.